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One of the things that attracted me to this new gig (art museum) I have (going on over four months now) was the opportunity to learn about equipment and systems that provide a precise level of temperature and humidity control. The museum, which has a vast photography collection, uses large refrigerated vaults to preserve the photographs, some of which are many decades old and irreplaceable if damaged. The equipment featured in this post is for the cold storage vault, which contains color photographs and negatives that through research has been shown to be best preserved at a temperature of 20°F and 30% relative humidity.

My boss, who has been at the museum since it reopened after a major renovation over four years ago, has been instrumental in getting this equipment dialed in from startup to today. He's quite pleased with the equipment's quality and performance and thought it merited inclusion in the Wall of Pride.

This first pic is of the Partlow combination chart recorder and temperature/humidity controller. The chart records for seven days; there is nearly a straight line for both temp and humidity, consistent with the numbers displayed in the red LED (20 degrees/30% RH). The Partlow controls a Munters air handler, a Drake liquid cooled chiller, and an air cooled DX unit that acts as a second stage to knock the discharge air temp down enough to achieve a 20 degree setpoint within the vault.
Dehumidificationm, in addition to two cooling coils, is accomplished by a dessicant wheel in the Munters AHU. This wheel is constantly reactivated by a blower passing heated air over the top portion of the wheel.

These two control boxes contain the components necessary to run the Munters air handler blower, dessicant wheel, and reactivation fan and heater elements.

This the right half of the Munters AHU. It is so long, it requires two photos to take it all in! A large reason for its length is the level of air filtration required for preservation of the photographs. The air filtration includes pleated, HEPA, Varicell, and carbon filters. Return air from the vault enters the AHU from the right, passes through the lower section of the dessicant wheel, then moves on through the series of filters and a chilled water coil before entering supply ducting.
In the middle of the pic is the chilled water storage tank and pump for the Drake chiller, which sits behind the tank.

Speaking of tanks, the sheetmetal used on the Munters AHU is thick. The entire array is built like a tank and has both a look and feel of quality. You can climb over this unit and the cabinet does not dent, bow, or even flex under your weight. Try doing that with most resi or light commercial split system AHU's!
Here's the second half, showing most of the housing for the various types of air filters.

Last but not least, the main workhorse of heat rejection for the vaults, a Drake chiller. This water cooled system uses a Copeland scroll compressor running R22. When online, the chilled water supply from this unit is below twenty degrees. The water that passes over the liquid cooled condenser gives up its heat to chilled water from the museum's central plant.
The compressor runs so cold on the Drake, it had to be insulated to prevent the shell from becoming a solid block of ice.

Not shown is an air cooled DX split system that is the final cooling element to get the vault down to twenty degrees.
As for any possible defrost issues with a system running this cold, when a proper reactivation is done on the dessicant wheel prior to starting or restarting the chiller, the cooling coils will NOT frost at all, due to the very low humidity levels and dew points. Therefore there is no need to stop the system occasionally to defrost both the chilled water and DX evap coils. This allows the system to run non-stop 24/7, rendering a precisely controlled environment, optimal for the preservation of the artwork.

10 tons of cooling equipment for a 150 sq ft room. The desiccant wheel adds a helluva heat load. The glycol in the chilled water circuit cuts efficiency too. Proportional control of the 3-way chilled water valve is how a very stable temperature is provided. Humidity control is also proportional. The return air is routed through or bypasses the desiccant wheel by a face and bypass damper arrangement.

Humidity contol is more important than the temperature control....any condensation on the prints and negatives...let's just say I'd be lookin for a new challenge elsewhere. and thanks for all not commenting on Shoppy's post at once. It gets so chaotic when that happens.

Originally posted by shophound Return air from the vault enters the AHU from the right, passes through the lower section of the dessicant wheel, then moves on through the series of filters and a chilled water coil before entering supply ducting.

Hi Mark...... The invitation is still open. There's a 2" pleated filter upstream of the desiccant wheel. It is kinda odd that the others are on the discharge side of the supply fan. The vault itself is like being inside of a walk-in cooler. Has the same heavy doors as a walk-in cooler. Very little people traffic in the vaults , so there's not much dirt and dust introduced into the vaults and they are sealed and insulated pretty tight. All the air handlers in the museum have more banks of filters than an average commercial air handler.

Here's a statistic.... there's over 1000 carbon filters in the building with an average weight of 12 lbs each.... 6 tons of carbon filters and our cost is $45,000 for a carbon filter change. Fortunately they last about 3 years between changes.

Originally posted by mark beiser If I had been now where I was 5 years ago, you would have had some more competition for that job shophound.

I'm sure you would've been good competition, judging by your posts.
Come on by for a visit when you can. I've been here over four months now and I still learn new stuff about the mechanics of this place all the time.